The invention relates to a propulsion system for a Hybrid Electrical Vehicle (HEV) or Electrical Vehicle (EV) comprising at least one Energy Storage System (ESS) and at least two Electric Motors (EM) The propulsion system is for example suitable for an articulated vehicle.
In recent years, development and commercialization of Hybrid Electric Vehicles (HEVs) and Electric Vehicles (EVs) that are effective in reducing fuel consumption and exhaust gases such as CO2 have been pursued. In order to reduce the environmental impact of a vehicle is it thus desired to use an electric propulsion system as much as possible and it should thus be preferred to use EVs only. However, there is a limit in the available range for such a vehicle due to the size and capacity of batteries mounted in the vehicles. One way of improving the range for a vehicle with an electric propulsion system is to provide the vehicle with an Internal Combustion Engine (ICE) so as to form a HEV. HEVs may thus provide a solution which may increase the range of the vehicle compared to an EV. However, the cruising range of a HEV in electric mode is in general even more limited than for an EV since the size and capacity of batteries mounted in the HEV is even smaller than for an EV. Hybrid vehicles must therefore use an engine and a motor in combination to secure a long cruising range.
For commercial vehicles, e.g. heavy load vehicle, construction equipment and public buses, may it be desirable to use more than one electric motor for propulsion of the vehicle in order to manage heavy loads and/or managing to drive where there are bad surface conditions. In particular may this be useful for a vehicle or vehicle composition forming a coupled vehicle in which several entities or modules are connected via one or several pivot able joints. Examples of such coupled vehicles may be an articulated vehicle or a vehicle train in which one or several trailers are connected to a leading vehicle. For such coupled vehicles there may be a desire to provide a traction force to the different articulated parts or trailers in order to improve traction and controllability of the coupled vehicle. An articulated vehicle is disclosed in US 2012/168234 in which there is provided an electric traction motor on each one of the two articulated parts. In this document is it also disclosed an example in which the same motor is powering driven wheels on both the articulated parts. However, there is a particular difficulty in providing a mechanical connection for transferring mechanical power between the different articulated parts of the vehicle or vehicle train. In this case is it somewhat easier to be able to transfer electric energy via the articulated connection, e.g. use stored electrical energy in a battery on a first articulated part and use it for motors located on the same articulated part and on another articulated part. However, there may be problems with wear of the wires in the articulation as well as the need for long wires such that it may be desired to avoid the need for connecting a battery to a motor located at a rather long distance from the battery. An example of a vehicle train having separate electric propulsion systems is disclosed in US 2014/052318. As disclosed therein is a separate battery and motor provided for each entity in the vehicle train. It may thus be generally considered, in particular if the articulated parts may be easily disconnected such as for a truck and trailer, to be unwise to have a battery dimensioned for a larger vehicle when a pivot able joint is disconnected and a module/entity of the vehicle is disconnected. In addition, the previous mentioned problems with wear of and need for long wires thus imply the use of separate electric propulsion systems on each vehicle.
Another important feature concerning the above described systems is the possibility to dimension and provide energy for the different propulsion units having different energy storage systems (ESS). In case there is one only energy storage system present, the energy consumption may easily be optimized to be distributed to the desired motor until the ESS is empty. In case there are different ESS present, the use of energy may be optimized in order to avoid that one of the ESS is depleted before another. The conjoint control of several separate ESS for a vehicle train is for example described in US 2014/052318. It is described therein how the unities are controlled to be recharged and discharged in order to keep a desired individual state of charge of the different ESS comprised in the vehicle train relative each other.
Hence, the invention is directed to the problem of designing and managing an electric propulsion system for a vehicle comprising at least two electric propulsion systems in order to manage the supply and storage of electrical energy, e.g. for a coupled vehicle comprising several vehicle entities or modules such as an articulated vehicle or a vehicle train.
The invention is thus directed, according to an aspect thereof, to a vehicle provided with an electric propulsion system (2). The vehicle may for example be a Hybrid Electrical Vehicle (HEV) or Electrical Vehicle (EV). The most commonly used HEV to day is the kind comprising an electrical propulsion system comprising an Electrical Motor (EM) and a commonly used mechanical powertrain connected to an Internal Combustion Engine (ICE). However, the basic principle for the invention is applicable regardless of which system the electrical propulsion system is combined with.
The system may be used for a wide variety of vehicles. By vehicles in this context is thus meant for example buses, construction equipment, lorries, combination of a truck and trailer, personal cars, commercial vehicles among others. The invention may thus be used for essentially any kind of vehicles even though there are some particular advantages when used for vehicles comprising a pivot able joint, e.g. an articulated vehicle, a truck and trailer combination or other combinations of vehicle modules connected to form a vehicle train.
The electrical propulsion system comprises a first Electrical Motor (EM1) for propulsion of the vehicle. The EM1 is provided with first Electrical Connections (EC1) designed to be connected to and powered by one or several electrical energy sources. Hence, the EM1 may be connected to one or several energy storages as well as sources for generating energy onboard or being connected to external power supplies. The EM1 is drivingly connected to at least one driven wheel in order to provide for a propulsion force to the vehicle. The EM1 may thus be connected to a single wheel, e.g. a wheel hub motor, or to one or several driven axles connected to wheels.
The electrical propulsion system also comprises a second Electrical Motor (EM2) for propulsion of the vehicle provided with second Electrical Connections (EC2) designed to be connected to and powered by one or several electrical energy sources. There is at least one driven wheel drivingly connected to the EM2. The EM2 may or may not be of the same kind as the EM1. The EM1 may for example be one of a pair of wheel hub motors and the EM2 may be a motor for powering a driven axle for another pair of wheels or both EM1 and EM2 may be designed and implemented in the electric propulsion system to power two different driven axles connected to respective wheels for each axle. EM1 and EM2 may also be wheel hub motors both of them configured to be connected to different set ups of electrical power supplies. In general, EM1 and EM2 have some difference in the set up of power supplies such that all electrical energy power sources are not the same for both motors. One motor could also provide power to more than one driven axle. There may of course also be further motors included in the electrical propulsion system if desired.
The electrical propulsion system also comprises an on-board Energy Storage System (ESS1) electrically connected to the first Electrical Motor (EM1) via said first Electrical Connections (EC1) in order to provide electrical power to the first Electrical Motor (EM1). The ESS1 may for example be a battery or a set of batteries or other entities able of storing electrical energy.
In order to control the electric propulsion system is there an Electronic Control Unit (ECU) incorporated in the system. The ECU may be a single processor or be a group of processors which together form the ECU. The ECU is programmed to control the electric propulsion system and the use of the EM1 and EM2. The use of the EM1 and EM2 is in general dependent on many parameters and may in particular be many differences dependent on if the vehicle is a HEV or EV. However, one essential parameter for controlling the motors EM1 and EM2 is the availability of electrical energy and the State Of Charge (SOC) for different on board energy storages. Hence, the motors EM1 and EM2 are controlled at least depending on the State Of Charge (SOC) level in the first Energy Storage System (ESS1). For example, there is a maximum level of charge over which further charging may cause damage to the ESS1 and the EM1 should thus accordingly be controlled to not be used for regenerative braking in order to regenerate the ESS1. The ECU is further programmed to control the operation of EM1 and EM2 in dependence of the availability of electrical energy for the EM2. The availability differs depending on which source/-s for providing energy that is/are present and able to be used at the moment. For example, the EM2 may be connected to a second Energy Storage System (ESS2) and in case there are no other sources connected to EM2, and the EM1 is only using ESS1 as a source for electrical energy, the ECU could be programmed to primarily use the electric motor connected to the energy storage system having the highest SOC level to be used for propulsion of the vehicle. This simplified model may of course be refined and take into account present, and estimated future, vehicle operation and driving conditions. In case there are further energy sources present, e.g. either (or both) of the electrical propulsion systems being able to use some kind of on-board generator, the possible maximum distance with the on board generated electricity may be taken into account. Hence, the overall possibility of the electric propulsion system, including two or more electric motors, to be supplied by electric energy as well as the possibility for supply of electric energy for each individual motor is evaluated. The system may be further refined by evaluating and estimating the different kind of sources for generating/using stored electric energy, when it is decided which motor or motors that should be primarily used for propulsion of the vehicle. In addition to the energy supply problem are also other parameters like safety and driving smoothness taken into account when controlling the use of motors and such parameters may set limits for how the electric motors may be used.
The electrical propulsion system may for example comprise power collectors adapted to be connected to an external power supply, e.g. electrically conductive rails on the ground or lines in the air, in order to supply electrical power to the system while the vehicle is travelling. In case not all electric storages on the vehicle have the possibility to be supplied by the external power source is the vehicle preferably controlled to primarily use the motors which may be supplied by electricity from the external source while travelling and being connected.
In order to enable an improved charging of one or several electrical Energy Storage Systems (ESS), e.g. batteries, in the electric propulsion system and/or controlling the distribution of the charge between several electrical energy storage systems to be more evenly distributed or distributed according to any other specific desire, may the Electronic Control Unit (ECU) be programmed to include an energy transfer mode. In this mode is it thus intended that the electrical propulsion system is controlled with a focus on the State Of Charge (SOC) of the electrical ESS and the distribution of charge between several such systems if present and other parameters such as driving comfort, speed and/or the overall energy efficiency may be set to be less important in this mode. In the energy transfer mode is the use of the second Electrical Motor (EM2) for propulsive force increased and the use of the first Electrical Motor (EM1) for regenerative braking is increased. This could mean the braking action from an EM, e.g. EM1, electrically connected to an ESS, e.g. ESS1, is used more frequently, during longer periods and/or used while applying a stronger braking force than when the vehicle is driven in other modes. In the energy transfer mode is thus the electric propulsion system controlled in order to reduce the consumption of electrical energy from, or even increase the SOC of, a selected ESS by regenerative braking at the cost of an increased use of another energy source for propulsive force. This means that the overall energy consumption may be allowed to be increased as a result of friction losses from using more propulsion and braking force than desired for the resulting propulsive force
The energy transfer mode may be selected manually or automatically. It may for example be possible to have indicators, e.g. indicating low SOC level in one ESS, e.g. ESS1, or uneven distribution of SOC between several ESS, e.g. ESS1 and ESS2, in order to advise a driver to select the energy transfer mode. At certain occasions may it not be desired to run the vehicle in an energy transfer mode, e.g. if the driver knows he soon will be stopping the vehicle and charging the vehicle over-night. There may also be some kind of semi-automatic system in which the driver may choose if the vehicle should be run in the energy transfer mode in certain conditions and having other conditions in which the vehicle is mandatory to be set in the energy transfer mode or not. One occasion when it should not be possible to use the energy transfer mode is when all Energy Storage Systems (ESS) have been recharged to a maximum allowable SOC limit and the energy transfer mode could be obligatory to be used to recharge an ESS when the SOC is below a certain SOC level, e.g. when the ESS is depleted and the vehicle is in a low temperature environment. However, the indication for or the automatic control to set the vehicle to run in an energy transfer mode is at least dependent on the State Of Charge (SOC) level in an electrical Energy Storage System, e.g. ESS1 which is electrically connected to EM1, which should be below a defined level in order to be recharged by regenerative braking. In addition, in order to assure that the energy transfer mode actually performs a desired action should it be estimated that there is more electrical energy available for propulsion of the vehicle in the electrical energy sources connected to another electrical motor, e.g. EM2, than the estimated available energy in the electrical energy sources connected to the electrical motor being used for regenerative braking, exemplified as EM1, in order to regenerate an ESS having a SOC below a predefined value, which was exemplified as EESI previously. The criteria for using the energy transfer mode could in somewhat simplified way be described as the system is controlled to recharge a first energy storage system by increased regenerative braking when there is a need or desire to recharge the selected energy storage system, e.g. due to a low state of charge, and evaluate and considering this need and compare with the present possibilities to use another electrical energy source for an increased use in providing electric energy to provide the overall propulsive force for the vehicle. Another way of explaining this feature could be to say that there is an increased use of regenerative braking in the energy transfer mode in order to regenerate a selected energy storage system while it is estimated that another energy source is better suited to provide electrical energy for a propulsive force to the vehicle, sometimes to the extent that it is even beneficial to provide braking in an excess of the total braking demand for the vehicle (when controlled in other modes) in order to regenerate the selected energy storage system even though there will be an increase in friction losses and a need to provide still extra propulsion force in order to compensate for the friction losses by another energy source.
There may be several different criteria set in order to decide when the energy transfer mode should be used. These criteria depend among other things on which electrical energy sources that are connected to the second Electrical Motor (EM2). The vehicle may for example be designed such that the EM2 is electrically connected to and powered by a second Energy Storage System (ESS2). In this case could the Electronic Control Unit (ECU) be programmed such that it is estimated that there is more electrical energy available for propulsion of the second Electrical Motor (EM2) when the available electrical energy in said second Energy Storage System (ESS2) is higher compared to the first electrical Energy Storage System (ESS1). This measure may for example be used when the ESS1 and ESS2 are of the same size and used equally during normal driving operations. The case may also be that one of the ESS, e.g. ESS1, is intended to be used mainly for propulsion and have a considerably larger storage capacity than the other ESS, e.g. ESS2, which is intended to provide an additional force only during certain occasions. In this case could the ECU be programmed to set the vehicle in the energy transfer mode in dependence of the relative SOC levels for the respective ESS, e.g. may the ECU be programmed to decide that the relative SOC levels should be set to be the same or that the SOC level for the smaller EES, e.g. ESS2, should be above a rather high limit, e.g. 75%, as long as the main ESS, e.g. ESS1, is above a lower level, e.g. 30%, in order to have the additional ESS ready to be used when needed during certain occasions. The levels could also be set in dependence on a predicted future use of the vehicle, e.g. by the use of sampled energy consumption for the respective ESS for a certain route or working cycles or by estimating the use of the respective ESS from GPS and map data for a predicted route. Hence, the ECU could be programmed such that it is estimated that there is more electrical energy available for propulsion of the second Electrical Motor (EM2) when the electrical energy in said second Energy Storage System (ESS2) is able to provide electrical power for propulsive force for a longer time than the first Energy Storage System (ESS1) may provide energy to the first Electrical Motor (EM1) for propulsion of the vehicle based on estimation of present or future vehicle operation conditions. The ECU could thus be set to estimate the future use of the respective Electrical Motors (there may be more than two) in the vehicle and in dependence of the SOC of the electrical Energy Storage Systems (there may also be more than two) and how the ESS are connected to the EM control the system in the energy transfer mode to control the propulsion and braking operations to get a desired SOC level of the respective ESS. In the examples given herein is the EM1 connected to the ESS1 and the EM2 connected to the ESS2 if not otherwise indicated. However, it shall be noted that one ESS may be connected to several EM. In addition, one EM may be connected to several ESS. The ECU could also be programmed such that it is estimated that there is more electrical energy available for propulsion by the EM2 when the ESS2 is able to provide energy with less reduction of the overall SOC of the on board ESS compared with using the ESS1 for providing electrical energy to the EM1. This could for example be the case if there is a source for generating electric energy in order to propel EM2 or charging ESS2. In the case of a Hybrid Electric Vehicle (HEV) and there is a possibility to directly provide a propulsion force to the same driven wheel as EM2 from another power source, e.g. an Internal Combustion Engine (ICE), could it also be decided that the there is more electrical energy available for the EM2 than the EM1 even though the SOC level in ESS2 actually is lower than in ESS1. Below follows further reasoning concerning the possibility to use other power sources to power an EM which may be used in addition to, or replacing, on board ESS. It shall be further noted that the energy transfer mode may be overruled by other modes, e.g. if a sport mode is selected is it most probably not desired to include more braking than needed or if some kind of snow/ice mode is selected should the braking most probably be adapted to provide most possible grip and allocate the braking actions for this purpose instead of controlling the braking to regenerate optimally as desired in the energy transfer mode. Likewise, the energy transfer mode should of course be overruled for braking actions, or propulsion forces, in order to drive the vehicle in a safe manner.
As disclosed briefly above, the vehicle may be adapted to use further sources, or further supplies, for electric energy than what is originally contained in the on-board electric Energy Storage Systems (ESS) when the vehicle starts. Such other sources may for example be liquid fuel which is used in an Internal Combustion Engine (ICE) or fuel cells using hydrogen to generate electricity for recharging an ESS or being directly connected to power an Electric Motor (EM). Hence, it may thus be decided that there is more available electrical energy for an EM being connected to such a supply as described than the available energy for another EM being connected to an ESS having more actual electrical energy stored. Another way of providing electrical energy is to use some kind of system for continuously supplying electrical power during travel, e.g. by using power collectors being connected to a stationary electrical grid by means of rails on the ground or wires in the air. In this case may the Electronic Control Unit (ECU) be programmed such that it is estimated that there is more available electrical energy for propulsion of the second Electrical Motor (EM2) when the EM2 and/or a second Energy Storage System (ESS2), electrically connected to the EM2, is receiving electrical power by the use of power collectors adapted to be connected to an external power supply (the stationary electrical grid) during travel for supply of electric power to the EM2 and/or the ESS2. In this case could it be considered that the available energy for the electrical devices connected to the grid is infinite and the system should thus primarily use EM2 for propulsion of the vehicle and the other EMs used for regenerative braking in order to charge storage systems connected to the other EMs. The ECU could for example be programmed to control the vehicle to use maximum possible propulsive force for the EMs connected to the grid (directly or via an ESS) and use the other EMs for regenerative braking. Alternatively, the load for regenerative braking is optimized for the EMs not connected to the grid and the EMs connected to the grid is set to be controlled to provide for the desired total propulsion and braking force. If the power collectors are electrically connected with an ESS, e.g. the ESS2, in order to recharge the ESS2 during travel is there an advantage in that the ESS2 may be charged also at standstill without the need of having a connected EM running for recharge of the ESS. However, it is probably most efficient to connect the power collectors to a so called junction box which is designed to direct the power from the power collectors to a suitable consumer, e.g. an EM, ESS charging or a Power Take-Off (PTO).
The system described above is in particular considered to be useful when there are several Electrical Storage Systems (ESS) on-board a vehicle which systems are electrically isolated from each other. In this case is there thus no possibility to transfer electric energy by electrical wires from one ESS to another ESS. Hence, the system may be used for a system as described above in which the first electrical Energy Storage System (ESS1) is electrically isolated from the electrical energy sources electrically connected to the second Electrical Motor (EM2), including ESS2 when present, such that there is no possibility to directly transfer electric energy to or from said first electrical Energy Storage System (ESS1) and the electrical energy sources electrically connected to the second Electrical Motor (EM2) or the other way around.
The system described above is also thought to be in particular suitable for systems in which at least one of the ESS (and an associated EM) is not adapted to be able to receive power from the grid during travel while at least another ESS (or an EM associated with the at least another ESS) is provided with power collectors for providing electric energy supply during travel of the vehicle. Hence, with reference to the earlier examples given, this is for example the case when the first Electrical Motor (EM1) lacks the possibility to be supplied by electricity from an external power supply during travel, either directly or via charging of an ESS, e.g. ESS1, and the second Electrical Motor (EM2) is connected via electrical connections to power collectors, either directly or via charging of the ESS2, adapted to be connected to an external power supply during travel. The Electronic Control Unit (ECU) may in this case be programmed to use the EM2 for propulsion of the vehicle, while being connected to the grid, simultaneously as the first EM1 is used for regenerative braking of the vehicle in order to charge the ESS1 when the vehicle is controlled in the energy transfer mode. This method, i.e. using regenerative braking for one motor while another motor is used for propulsion, may of course also be used when the vehicle not is connected to the grid or for other designs of the vehicle as described above.
The vehicle described above may be designed such that the EM1 is drivingly connected to at least a first driven wheel different from at least a second driven wheel being drivingly connected to the EM2. The vehicle could for example be an articulated vehicle in which the EM1 is drivingly connected to a first driven wheel on a first part of an articulated vehicle and the EM2 is drivingly connected to a second, different driven wheel on a second part of an articulated vehicle wherein said first and second parts of the articulated vehicle are on different sides of an articulation of said vehicle. The vehicle could be arranged such that the EM1 is drivingly connected to a first driven axle connected to the first driven wheel and the EM2 is drivingly connected to a second driven axle connected to said second driven wheel.
The vehicle could also be designed such that the first and second Electric Motors (EM1, EM2) are drivingly connected to a common driven wheel, e.g. by powering the same driven axle being connected to said driven wheel. To be noted, this design could be used together with the design in which the EMs are also connected to separate driven wheels, e.g. if there are three driven axles and the EM1 is connected to a first driven axle, the EM2 is connected to a second driven axle and both EM1 and EM2 are connected to a third driven axle. As an alternative, either of the EM1 or EM2 could be disconnected from being drivingly connected to the first respectively second driven axles such that one of the Electric Motors only is drivingly connected to the common (third) driven axle. In this case could the third axle be used for transfer electrical energy to either of the ESSs, e.g. ESS1, by using EM2 for propulsion power to the third axle while EM1 is used to provide a braking torque to the third axle for regeneration of electrical energy in the ESS1. In this case may there thus be an energy transfer without the need to provide a torque for propulsive power to a first driven wheel and a braking force to a second driven wheel causing an increased wear of the tires but instead using the third axle as the power transferring element.
Hence, there are several different designs for which the system is suitable. And it shall be noted that in the above examples have a vehicle comprising two electric motors (EM) been described for the sake of simplicity when giving examples. However, the skilled person understands that there may be further EMs in the system which easily may be integrated and controlled according to the ideas described herein.
The invention further relates to a method for controlling an electric propulsion system for a vehicle, e.g. a Hybrid Electrical Vehicle (HEV) or Electrical Vehicle (EV). The propulsion system comprises a first Electrical Motor (EM1) and a second Electrical Motor (EM2) for propulsion of the vehicle. The EM1 respective EM2 are provided with first Electrical Connections (EC1) respective second Electrical Connections (EC2) designed to be connected to and powered by one or several electrical energy sources. There is at least one driven wheel drivingly connected to the EM1 and at least one driven wheel drivingly connected to the EM2. The system also includes a first electrical energy source being an on-board Energy Storage System (ESS1) electrically connected to the EM1 via said first Electrical Connections (EC1) in order to provide electrical power to power the EM1. For control of the propulsion system is an Electronic Control Unit (ECU) included.
The method comprises the features of controlling the use of the EM1 and the EM2 (and possibly further EMs) in dependence of the State Of Charge (SOC) level in the ESS1 (and possibly further ESSs) and the availability of electrical energy for the EM2. In a generalized form this may be expressed as the control of the EMs in the electric propulsion system is dependent on the availability of electrical energy for the EMs.
The method is further defined by the feature that it comprises an energy transfer mode in which the use of the EM2 for propulsive force is increased and the use of the EM1 for regenerative breaking is increased. The energy transfer mode may be selected manually from indicating means disclosing regenerative mode is desired due to uneven distribution of charge between on board ESS and/or that there is a lot of electric energy available for at least one of the electric propulsion systems. The system may also be set to be triggered automatically in dependence of certain criteria. These criteria are that it is indicated the State Of Charge (SOC) level in at least one on-board ESS, e.g. the first electrical Energy Storage System (ESS1), is below a defined level and, in addition, that it is estimated there is more electrical energy available for the second Electrical Connections (EC2), connected to the second Electrical Motor (EM2), than for the first Electrical Connections (EC1) connected to the EM1. The automatic selection may comprise further parameters in order to change over to the energy transfer mode. Since there in general is some drawback in using the energy transfer mode, e.g. a loss of energy in the transfer and/or not being able to control the vehicle optimally concerning comfort and optimal braking during certain conditions, is it generally preferred that the energy transfer mode not is used, or at least started until there is a real need for the energy transfer mode. It may also be possible to have different levels of energy transfer mode depending on the need or desire to recharge a certain ESS, e.g. may it be allowed to use one EM for propulsion while another is used for regenerative braking when there is a strong urge to recharge a certain ESS and when there is a less need for recharging the energy transfer mode may be more moderately used and the necessary braking and propulsion operations are controlled to be performed by a suitable EM in order to recharge or distribute the electric energy charge to the on-board ESS.
To be selected manually there may be options which not may be overruled, e.g. if all ESS which may be the target for regeneration already are above a critical level for being further charged or that the propulsion is set to provide optimal traction and braking performance due to slippery driving conditions.
The control method may be defined such that it is estimated that there is more available electrical energy for propulsion of a selected Electrical Motor (EM), e.g. the EM2, when the selected EM and/or an Energy Storage System (ESS) electrically connected to the selected EM, e.g. the ESS2, is receiving power during travel via its associated electrical connections, e.g. the second Electrical Connections (EC2), by the use of power collectors. The power collectors are connected to an external power supply such as the public grid (mains) for supplying electric power to the second (EM2) directly or via the ESS2. The electric power may be transferred from the mains to the vehicle by means of power collectors in the shape of roof mounted pantographs intended to be in contact with wires in the air or contact shoes mounted to be in contact with a rail on the ground.
The method may include the feature of controlling at least one of the EMs, e.g. EM1, during a time period to be used for regenerative braking of the vehicle to an extent exceeding the total braking demand for the vehicle during normal control mode of the vehicle during said time period in order to charge an ESS connected to the EM1, e.g. ESS1. In order to compensate for the braking action is the propulsion force compensated by another EM, e.g. the EM2, is controlled during said time period to provide a propulsive force being larger than the total propulsion demand during said time period. In case the vehicle is a Hybrid Electrical Vehicle (HEV) could the propulsion force instead be provided by the other propulsion system, e.g. by an Internal Combustion Engine drivingly connected via a power train to a driven wheel.
The method described above may include the feature of controlling a propulsion unit, e.g. the EM2, to provide a propulsion force to the vehicle simultaneously as an EM, e.g. the EM1, is used for regenerative braking of the vehicle in order to charge an associated ESS, e.g. the ESS1.